Automatic transmissions in automobiles comprise a torque converter, a wet multi-plate clutch, a gear mechanism, and a mechanism controlling these elements. The torque transmission capacity is automatically set according to the speed of automobile and the degree of load. Modern automatic transmissions further comprise a lockup clutch mounted to the torque converter, so as to improve fuel economy. The use of the lockup clutch enables engine torque to be transmitted to the automatic transmission according to driving conditions in addition to the driving force transmitted through a lubricating oil. However, since the torque variation produced by the operation of the lockup clutch sometimes disturbs passengers due to shudder, the lockup clutch is generally set to operate only under high speed driving conditions giving less torque variation.
Under low speed driving conditions as when an automobile starts, loss of driving force transmission is caused between the engine output revolution and the transmission input revolution. Therefore, enough improvement of fuel economy is not attained. Accordingly, automatic transmissions adopt a slip control system by which the lockup mechanism can operate under the low speed driving conditions and the transmission loss can be reduced. However, when the clutch is subjected to control by the slip control system, abnormal vibration of the body of automobile (i.e., shudder) takes place on the friction surface of the lockup clutch. At low road speeds vehicle operation is rough and engine vibration is transmitted through the drive train. Rough operation and engine vibration are not acceptable to drivers.
Shudder occurs when the sliding rate (V) in the lockup clutch increases and the coefficient of friction (μ) decreases. Thus, it is desirable to employ a lubricating oil (automatic transmission fluid) which shows a favorable μ-V character, i.e., the friction coefficient increases when the sliding rate increases, and keeps the favorable μ-V character for a prolonged period of time, i.e., prolonged shudder inhibition performance.
JASO (Japanese Automobile Standard Organization) M349:2001 describes a standard oil T-III which shows standard shudder inhibition performance and transmissive torque capacity. However, there is given no information with respect to formulation of the T-III standard oil.
Prolonged shudder inhibition can be attained by incorporating a friction modifier (generally, friction decreasing agent). However, if too much friction modifier is incorporated into a lubricating oil, the friction coefficient of the wet clutch extremely decreases and hence enough transmissive torque capacity cannot be obtained.
U.S. Pat. No. 4,948,523 discloses a lubricating composition, preferably essentially free of zinc dihydrocarbyldithiophosphate compounds, and optionally free of chlorine containing silver lubricity agents, comprising a major proportion of an oil of lubricating viscosity and a minor amount of a silver protective agent comprising the reaction product of a C5 to C60 carboxylic acid and at least one amine selected from the group consisting of (1) guanidine, urea, and thiourea compounds; (2) C1 to C20 hydrocarbyl or hydroxy-substituted hydrocarbyl mono-amines, alkylene diamines, and (3) polyalkylene polyamines; and N-alkyl glycine.
U.S. Pat. No. 5,395,539 discloses certain hydrocarbon soluble or dispersible amide reaction products (Component-1), and mixtures, and/or acid amine salts of Component-1 and certain acid/esters (Component-2), which are useful as friction modifying additives for oleaginous compositions such as lubricating oils, including power transmitting fluids, particularly automatic transmission fluids (ATF), and to the oleaginous compositions in which they are contained.
U.S. Pat. No. 5,916,852 discloses lubricating fluids which include an additive combination comprising a compound having the general formula R—NH2 with oil-soluble phosphorus compounds, an ashless dispersant, and, optionally, other amine containing friction modifiers provide lubricating fluids which exhibit excellent break-in characteristics that are capable of preventing green shudder in automatic transmissions.
U.S. Pat. No. 6,303,547 discloses lubricant formulations containing the reaction product of at least one C5 to C60 carboxylic acid and at least one amine selected from the group consisting of guanidine, aminoguanidine, urea, thiourea and salts thereof is useful as a gear oil additive. The lubricant formulations exhibit excellent low and high temperature rheology and are particularly suited for use in automotive and industrial gear applications. Lubricants of the present invention exhibit improved performance properties, such as increased axle efficiencies and lower axle temperatures, improved limited slip performance, reduced chatter, improved frictional durability and/or improved power divider performance compared to lubricant formulations that do not contain said reaction products.
Japanese Patent Publication No. 2001-247532 discloses fatty acid amide compounds used for surface lubricant, vehicle component and thermal recording materials, has three or more amide groups in a molecule having the formula R1CONH(CH2)m((NCOR2)(CH2)n)lNHCOR3, where R1-R3 is a C12 to C50 alkyl or alkenyl group, m and n=1-3, and l=1-4.
U.S. Patent Application Publication No. 2002/0072478A1 discloses a lubricating oil and one or more succinimide-modified compounds having long-lasting anti-shudder property, enhanced transmission torque capacity for a wet clutches and/or wet brakes, and an excellent shifting property for automatic transmissions and continuously variable transmissions.
Japanese Patent No. 3330245 discloses lubricating oil compositions for slide guide surfaces containing nitrogen-containing compounds of polyamines and amides in mineral and/or synthetic oil.